In general, the invention relates to damper assemblies for use in vehicle suspension systems, and more particularly, to a damper piston including a bypass valve assembly for a damper or magnetorheological shock absorber or monotube strut.
Current vehicle suspensions frequently incorporate dampers, i.e., shock absorber and strut assemblies as both a damping device and, in some applications, part of the suspension""s load bearing structure. Dampers are conventionally known which include a piston with a connected piston rod. The piston is slidably contained in a fluid filled tube or chamber.
Such vehicle suspension dampers, used to control vehicle ride and handling, typically contain control valves tuned to control vehicle jounce (compression of damper) and rebound damping (extension of damper) independently. It is generally known that it is desirable to have jounce damping set at approximately one-half to one-third the level of rebound damping. To an extent, in a current design damper provided with magnetorheological features, damping can be externally controlled. Generally, this is accomplished by providing the damper with a magnetorheological fluid, which when exposed to a magnetic field, provides a condition of increased resistance to flow or apparent viscosity in the damper, and thus an increased damping effect. However, the range of damping available from the damper is the same for jounce and rebound.
A type of damper, commonly known as a xe2x80x9cMcPherson Strutxe2x80x9d, is commonly used to damp motion of the suspensions of motor vehicles. These struts function with a side load applied between the exposed end of the piston rod and the body of the strut. Within the strut, this side load results in loading at two locations where relative motion occurs. One location is a bearing on the rod guide through which the piston rod slides. The other location is a bearing formed on the exterior of the piston where it slides against the cylinder tube. To minimize loading at these locations, it is desirable to maximize the distance between the rod guide bearing and the piston bearing. Conventional struts are designed so the piston strokes as close to the base of the strut as in practical, maintaining any allowable dead length (length not usable as travel) as part of the distance between the rod guide bearing and the piston bearing.
It would be desirable to provide jounce and rebound control in a strut that provides improved loading control that overcomes the above and other disadvantages.
One aspect of the present invention provides an adjustable vehicle suspension strut assembly configured to be arranged between a wheel assembly and a body of a vehicle. Accordingly, the present invention provides an adjustable strut including a tube including a magnetorheological fluid, a piston rod positioned in the tube and a piston assembly attached to an internal end of the rod. The piston assembly includes a magnetorheological passageway and a valve assembly. The valve assembly is positioned at a point upstream of the internal end of the piston rod. The valve assembly provides a second passageway for allowing flow of magnetorheological fluid therethrough during a compression stroke of the strut.
Other aspects of the present invention provides a piston assembly including a core positioned on the piston rod and a flux ring positioned about the core that defines the magnetorheological passageway therebetween. The core may include a coil attached thereto, with the coil being positioned adjacent the magnetorheological passageway for producing a magnetic field thereacross. The magnetic field produced across the magnetorheological passageway may change the apparent viscosity of at least a portion of magnetorheological fluid present therein. The valve assembly can include an annular valve seat, an outer surface of the valve seat slidably contacting an inner surface of the tube.
The valve assembly is positioned upstream of the magnetorheological passageway. The second passageway may be formed in the valve seat. The flux ring may be spaced apart from the tube to define a third passageway, the third passageway being in fluid communication with the second passageway to allow fluid flow therethrough. The flux ring and valve assembly may be attached by a cap member.
The cap member may include a first end for threadable connection to the flux ring and a second end for threadable connection to the valve assembly. The valve assembly is permitted to open during compression strokes of the damper and is substantially closed during extension strokes of the damper. The valve assembly may include a first disc that permits a first amount of flow through the control valve during both compression strokes and extension strokes of the damper. The first disc can be a washer including a plurality of outer notches. The first disc may permit a second amount of flow through the control valve during compression strokes, the first amount of flow being less than the second amount of flow. The first disc may be biased against a valve seat portion of the control valve by a spring member. The spring may be one of a wavy washer and a Belleville washer. The second disc may be positioned between the first disc and the spring member.
Another aspect of the present invention provides a method of controlling an adjustable damper including enclosing a piston in a magnetorheological fluid, providing a first passageway in the piston, generating a magnetic field in the first passageway of the piston to produce an apparent viscosity change in the magnetorheological fluid responsive to the magnetic field, providing a second passageway in the piston at a portion of the piston upstream of the first passageway and controlling the fluid flow through a second passageway of the piston. Controlling the fluid flow through the second passageway may include providing a first flow-through the second passageway during an extension stroke and providing a second flow-through during a compression stroke, the first flow being substantially less than the second flow.
Another aspect of the present invention provides an adjustable damper including means for enclosing a piston in a magnetorheological fluid, means for providing a first passageway in the piston, means for generating a magnetic field in the first passageway of the piston to produce an apparent viscosity change in the magnetorheological fluid responsive to the magnetic field, means for providing a second passageway in the piston at a portion of the piston upstream of the first passageway and means for controlling the fluid flow through a second passageway of the piston.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of the presently preferred embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.